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Minerals Minerals Minerals are solid, inorganic substances found in the Earth’s crust. What is a Mineral? Characteristics of Minerals: Naturally Occurring Inorganic Solid Definite Chemical Formula Definite Crystal Structure Naturally Occurring Formed by natural processes (not in the laboratory). - Is an ice cube a mineral? - Is the ice on the windshield of a car a mineral? Inorganic Formed by inorganic processes; not living. Does not contain chains of carbon atoms. Solid Not gas or liquid. -H2O as ice in a glacier is a mineral, but water is not. Definite volume and shape. Definite Chemical Formula Minerals are expressed by a specific chemical formula: -Gold (Au) -Calcite (CaCO3) -Quartz (SiO2) -Pyrite (FeS2) Definite Crystal Structure A crystal is a solid in which the atoms are arranged in repeating patterns. Some mineral specimens have flat surfaces and sharp edges, showing distinct crystal shapes on the outside. Even if a mineral doesn’t show its crystal shape on the outside, its atoms are still arranged in an orderly crystal structure. Composition of the Earth’s Crust An element is made of one atom and a Compound is two or more elements together Eight Elements make up over 98% of Earth’s Crust: -Oxygen (O) 46% -Silicon (Si) 28% -Aluminum (Al) -Iron (Fe) -Calcium (Ca) -Sodium (Na) -Potassium (K) -Magnesium (Mg) Minerals are always single chemical compounds or pure elements. Where Do Minerals Come From? Magma Evaporation Of the almost 4000 known minerals, only about 100 are common. The most common are quartz,feldspar,mica, and calcite. How Are Minerals Identified? Color Texture Luster Hardness Streak Heft Crystal Form Cleavage and Fracture Special Properties Color Usually the first and most easily observed. Sometimes very helpful for ID, sometimes not much help at all. -Some minerals are always the same color (malachite = green, azurite = blue). -Some minerals can have many colors (quartz = white, clear, purple, pink, yellow, gray). ROSE QUARTZ QUARTZ SMOKY QUARTZ Texture How a mineral feels to your touch. -For example: Some minerals feel greasy or soapy. Luster General appearance of a mineral surface in reflected light. Minerals can be classified as either metallic or non-metallic luster. Glassy-Obsidian Luster Non-metallic luster can be broken down into several types: -Glassy (Vitreous)– looks like glass. -Silky – shines like a silk cloth. -Pearly – looks like pearls. -Adamatine – brilliant, diamond-like shine. -Greasy – looks like its covered with oil. -Dull/Earthy – no apparent “shine”. Hardness Resistance to scratching by different items; “scratchability”. Mohs Hardness Scale 2.5 3.5 4.5 ~5 5.5 6.5 7 Fingernail Penny Nail Steel of a pocket knife Window Glass Steel file Quartz crystal Ex: If an unknown mineral can scratch a penny but can’t scratch glass, we would say its hardness is between 3.5 and 5.5 Mohs Mineral Hardness Scale 1) Talc Softest 2) Gypsum 3) Calcite 1 8 4) Flourite 5 5) Apatite 2 6) Feldspar 7) Quartz 9 6 8) Topaz 3 9) Corundum 10) Diamond 7 Hardest 4 10 Streak The color of a finely powdered mineral. Determined by rubbing the mineral on a streak plate. It may or may not be the same color as the mineral Heft The amount of matter in a given space. Mass/Volume = Density. Crystal Form Minerals have a characteristic crystal shape resulting from the atomic packing of the atoms when the mineral is forming. The shape of crystals, if present, can be very helpful in ID. A mineral sample often may not have crystals large enough to see. Cleavage and Fracture How a mineral breaks: Cleavage is the tendency of a mineral to split or crack along parallel or flat planes (even breaking). Fracture occurs when a mineral breaks at random lines instead of at consistent cleavage planes. (uneven breaking). Special Properties Magnetism (Magnetite) Glowing under ultraviolet light (Fluorite) Salty taste (Halite) Magnetite Smell (Sulfur) Reaction to HCl (Calcite)